EEPROMs are non-volatile memory devices which are erased and programmed using electrical signals. In general, an EEPROM cell, such as a FLOTOX (floating gate-tunnel oxide) cell, includes a floating gate transistor and a select transistor. The select transistor generally selects which individual cells of the EEPROM device are erased and programmed at a particular time.
CMOS devices may be used to implement a variety of discrete logic components and other digital devices, such as various types of RAMS, microprocessors, shift registers, sense amplifiers, etc. Generally, however, many of the processing steps for making an EEPROM device differ from the processing steps for making CMOS devices.
Conventional approaches to forming both EEPROM devices and CMOS devices on a single die generally comprise forming the EEPROM devices while masking the area(s) for the CMOS devices, then masking the EEPROM devices and forming the CMOS devices separately, or vice versa. This approach requires a total number of steps generally equal to the steps required to form each device on separate dice. While some basic steps may be performed simultaneously, it is generally difficult to integrate the steps of the EEPROM and CMOS processes.